<!DOCTYPE html>
<style>
.wwwc{
    font-size: 18px;
    color: #ffffff;
    background-color: blue;
    text-align: center;
}
</style>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>

<body>
<div id="test" class="wwwc"/>
</body>
<script>
    var test = document.getElementById('test');
    test.style.backgroundColor='red';
    test.innerHTML='文本已有修改'

</script>
</html>